Historically, the development of railguns was stymied by the lack of suitable power supplies to drive them. In the last decade or so, that situation has changed and successful railguns have been powered by homopolar generators, explosively driven magnetic flux compression generators, and capacitors. Each of these energy storage/generator devices is suitable for various railgun applications, but for railgun systems capable of launching large masses ballistically from the earth's surface into space, something better is required. Therefore, the requirement for a reusable flux compressor capable of charging a 50MJ inductor with a current of 4MA, and one possible design, are examined.